1. Field of the Invention
The present invention relates to a charged-particle beam instrument having a plurality of deflectors cooperating to cancel out their mutual deflection aberrations or oblique incidence.
2. Description of Related Art
In recent years, electron beam lithographic systems have become indispensable for manufacture of semiconductor devices.
FIG. 1 schematically shows one example of such an electron beam lithographic system. The system has an electron source 1 (such as a crossover point in an electron gun, an aperture irradiated with an electron beam and used to shape the cross section of the beam, or an image of the crossover point or the shaping aperture), a demagnifying lens 2 for forming an image of the electron source, and an objective lens 3 for focusing the image formed by the demagnifying lens 2 onto a workpiece 5 placed on a stage 4.
A deflector 6 is used such that an electron beam hits a position on the workpiece based on data about a pattern delineation position (hereinafter may be referred to as the pattern delineation position data). That is, the deflector 6 determines the position of the image formed on the workpiece 5. The stage 4 is driven by a stage-driving mechanism 7.
A controller 8 sends a deflection signal corresponding to the pattern delineation position data to the deflector 6 via a D/A converter 9 and via an amplifier 10. The controller 8 also sends a stage-driving signal to the stage-driving mechanism 7 via a D/A converter 12.
A blanking mechanism 13 is composed of a blanking deflector 14 and a blanking plate 15, and acts to blank the electron beam coming from the electron source 1 in response to a blanking signal based on pattern delineation time data sent in from the controller 8. For simplicity of illustration, only one deflector 6 is shown. In practice, there are deflectors for deflections in the X- and Y-directions, respectively. Similarly, there are stages 4 for motions in the X- and Y-directions, respectively.
In the lithographic system of the construction described above, when an actual semiconductor pattern is delineated, the electron beam from the electron source 1 is focused onto the workpiece 5 by the demagnifying lens 2 and objective lens 3. Under this condition, the beam is deflected by the deflector 6 according to the deflection signal based on the pattern position data from the controller 8 to write a desired pattern at a desired location on the workpiece 5.
When the electron beam is deflected by the deflector, deflection aberrations, such as deflection comatic aberration and deflection chromatic aberration, are produced. Furthermore, in such electron beam deflection, there is the problem of oblique incidence on the surface of the workpiece. A known method of suppressing such deflection aberrations and/or oblique incidence consists of mounting an additional deflector and canceling out deflection aberrations in the mutual deflectors and/or oblique incidence (see, for example, JP 59083336).
Even with the electron beam lithographic system shown in FIG. 1, in a case where the electron beam is deflected by the deflector 6, deflection aberrations and oblique incidence take place in the same way as in the foregoing case. This deteriorates the accuracy of deflection and lithography. Accordingly, as shown in FIG. 1, a second deflector 16 is disposed between the demagnifying lens 2 and the first deflector 6 on the electron beam path. The deflectors are cooperated to cancel out the deflection aberrations created by the mutual deflectors and/or oblique incidence. That is, the controller 8 applies a deflection voltage for canceling the aberration in the first deflector 6 and/or oblique incidence to the second deflector 16 via a D/A converter 17 and amplifier 18.
As the aberrations and/or oblique incidence is corrected in this way, the position on the workpiece 5 irradiated by the electron beam varies. Therefore, the deflection voltages to the first deflector 6 and second deflector 16 are determined such that the irradiated position (beam position) remains unchanged.
When the deflection aberrations due to the mutual deflectors are canceled out by cooperation of the first deflector 6 and second deflector 16 as described above, the deflection aberrations are equal in magnitude but opposite in sense (sign). Therefore, where the deflection aberration produced by the first deflector 6 is larger, it is necessary to increase the deflection aberration produced by the second deflector 16 accordingly.
For example, if the deflection range of the electron beam covered by the first deflector 6 is increased to enhance the throughput of the pattern delineation, the deflection aberration increases accordingly. Therefore, the deflection aberration produced by the second deflector 16 must be increased accordingly. The same principle applies to the case where the oblique incidence is canceled out.
If the center position of deflection is not varied, the magnitude of deflection aberration produced by a deflector is determined by the deflection angle. That is, the magnitude depends on the length (electrode length) of the electrode forming the deflector taken along the center axis, electrode-electrode distance (inside diameter of the electrode assuming that the deflector is made of a cylindrical electrode), and the voltage (deflection voltage) applied to the electrode. Accordingly, the deflection aberration is increased by (1) increasing the length of the electrode, (2) reducing the inside diameter of the electrode, (3) increasing the deflection voltage, or (4) using a combination of them.
However, in the optical system shown in FIG. 1, it is difficult to increase the electrode length of the second deflector 16 because of spatial restrictions. Furthermore, if the inside diameter of the electrode of the second deflector 16 is reduced, the inner surface of the electrode is brought accordingly closer to the optical axis of the electron beam. Consequently, the problem that deposition of contaminants arises from scattering electrons tends to be produced more easily. Also, charging effects tend to be produced more frequently.
In addition, in order to improve the throughput, higher-speed operation is necessary. For this purpose, the deflection voltage should be lowered. From this viewpoint, increasing the deflection voltage of the second deflector 16 greatly will result in a detrimental effect.